Micro-Electro-Mechanical Systems (MEMS) based thermal sensors are known in many different configurations. A basic MEMS flow sensor includes a heater and at least one temperature sensor in the near vicinity to detect heat fluctuation as fluid moves over the heater and temperature sensor(s). The rate of fluid movement over the heater and temperature sensor(s) can be used to determine flow rate.
Existing MEMS flow sensors utilize a heater and temperature sensors on a single plane inside the flow channel on a diaphragm or suspended bridge. One known form of flow sensor is shown in FIG. 1A in which a heater 10 and temperature sensors 12 are supported on a diaphragm or membrane 14 which is disposed in a flow channel 16. Another known version of a flow sensor is shown in FIG. 1B in which a heater 10A and temperature sensors 12A are formed in a silicon plate 18 which is placed in a flow channel 16A. The sensing of temperature in only one plane limits the performance of the device. Thermal convection is omnidirectional and sensing in only a single plane is inefficient.
A raw response curve from thermopiles on a single plane MEMS sensor is typically in the shape of a square root function with sensitivity highest at low flow and gradually decreasing as flow increases. This square root shape reflects the inefficiency of the etched conductors on a single plane.
It would be beneficial to have a thermal flow sensor with improved thermal efficiency, sensitivity and measuring range.